A typical printing apparatus (that is, a printer) operates upon principle of mixing colored ink or toner particles and allowing the mixed particles to be adsorbed into a printing paper. Although conventional printers are widely used in many fields, they require different color inks and/or toners to express a variety of colors and entail difficulties in modifying or amending printed output (which was already obtained through printing).
In order to overcome restrictions of conventional printing technologies as described above, a number of studies and investigations have been implemented and various techniques have been introduced. A representative example of products resulted from such studies is ‘electronic-ink.’ Electronic ink is a coloring device to express specific colors by applying an electric field to a capsule containing different color particles (e.g., black and white) having negative charge (−) and positive charge (+), respectively, to thereby indicate various kinds of information including, for example, text. However, such an electronic ink entails difficulties in expressing a variety of colors, since the expressed color of the particles is fixed to a specific predetermined color.
Accordingly, in order to solve the problems of conventional technologies described above, numerous methods have been proposed and, among these, a technique based on a principle of photonic crystals may be employed.
Photonic crystal is a substance or crystal expressing color at a specific wavelength by reflecting light at the specific wavelength while passing light in other wavelengths. Representative examples of such photonic crystals may include the wings of butterfly, the shell of Cyphochilus, etc. These substances have unique structures, in turn expressing specific colors, although pigments are not contained therein.
According to recent research on photonic crystals, compared to existing photonic crystals present in nature that generally reflect light at specific wavelengths, artificially synthesized photonic crystals containing proper materials may modify a crystal structure (for example, interlayer thickness for formation of photonic crystals) by external stimulation. As a result, wavelengths of reflected light may be desirably controlled in the UV and infrared regions as well as in the visible light region.
The inventors of the present invention have conceived that a printing medium, printing method and/or printing apparatus using photonic crystal characteristics of reflecting light at specific wavelengths may be successfully embodied by applying an electric field or a magnetic field to particles with electric charge or magnetic properties to control inter-particle distances of the particles and then by applying energy or blocking the energy application to the medium to fix the inter-particle distances of the particles. The present invention has been completed based on the foregoing ideas.